The present invention relates to a protection system, a layer 2 function block, a node and a ring network that are employed when the effective use of bandwidths (channels) is made by carrying out link aggregation in a ring network having a working channel and a protection channel, and in particular, to a protection system, a layer 2 function block, a node and a ring network by which traffic that is transmitted using the protection channel by means of the link aggregation when no failure exists in the network can also be transmitted when failure exists in the network, without abandoning the traffic.